1. Field of the Invention
The present invention relates to a semiconductor memory device, and particularly, to a semiconductor memory device including a non-volatile memory circuit and a plurality of different types of volatile memory circuits.
2. Description of the Background Art
In recent years, a multi-chip package (MCP) has been used in which a plurality of semiconductor chips are stored in one package. For example, in a portable information terminal such as a portable telephone having a strict requirement for size reduction, the mounting area of the semiconductor memory device must be reduced, and therefore MCP has actively being employed.
FIG. 22 schematically shows the configuration of a conventional semiconductor memory device 600.
Referring to FIG. 22, semiconductor memory device 600 employs a multi-chip package in which a static random access memory (SRAM) 602 and a flash memory 604 are stored in one package. SRAM 602 receives supply of a power-supply potential VS2, at a power-supply pad 606 on the chip, from the outside of the package via a power-supply terminal 610. Flash memory 604 receives supply of a power-supply potential VS1, at a power-supply pad 608 on the chip, from the outside of the package via power-supply terminal 612.
Thus, conventionally, power-supply terminal 610 corresponding to SRAM 602 and power-supply terminal 612 corresponding to flash memory 604 were separately provided in semiconductor memory device 600, to supply externally-applied power-supply potentials to the two respective memories independently of each other. Therefore, for example, the power-supply to a memory not accessed in the stand-by state of a portable terminal was stopped in order to reduce stand-by current and to extend continuous service hours of the battery.
In an example where the conventional semiconductor memory device 600 as shown in FIG. 22 is used for e.g. a portable telephone, the power-supply potential may be supplied only to SRAM 602 in the stand-by state where no conversation is being made, and supplying of the power-supply potential to flash memory 604 may be stopped, in order to reduce the stand-by current.
An SRAM mounted on semiconductor memory device 600 is characterized by high-speed operation and small stand-by current. Whereas, a flash memory mounted to semiconductor memory device 600 in a similar manner is characterized in that data can be held in a non-volatile manner even though the supply of power-supply potential is stopped. However, the flash memory also has characteristics such that the stand-by current is somewhat larger than that of SRAM, and that data rewriting cannot be performed as fast as SRAM, since it takes time to erase data. Taking these two memory characteristics into consideration, reduction of consumption current has been attempted by applying the power-supply potential only to a requiring memory.
An example of a memory capable of faster operation compared to the flash memory is a dynamic random access memory (DRAM). The memory cell of the DRAM is smaller in size compared to that of SRAM, and the cost per bit is less expensive than that of SRAM. However, SRAM has been used, rather than DRAM, in a portable information terminal or the like having a strict requirement for size reduction, in order to simplify the system configuration.
This is because DRAM holds data as electric charge in a capacitor of a memory cell, and hence, rewriting, i.e. refreshing, is required in a certain cycle in order to continue holding the data. The DRAM also requires complex control related to the refreshing, such as refreshing operation per refresh cycle, and waiting for access to a memory under refresh until the end of the refresh cycle. SRAM is used since it requires no complex control as required in DRAM and thus can simplify the system configuration.
However, in recent years, the function of the portable information terminal has vastly been improved so as to also handle image data. Thus, a large capacity of memory function has increasingly been required. In such a case, use of SRAM having a memory cell size 10 times larger than that of DRAM would increase the chip size in order to realize the memory with a large capacity. The increase of the chip size would not only raise the cost of the portable information terminal, but also would increase the mounting area of the memory.
Then, a memory that can be accessed in a manner similar to that of SRAM by using small memory cells of DRAM, e.g. pseudo-SRAM, may be used in place of the conventional SRAM. However, the memory cells of DRAM requires refresh, which results in larger stand-by current compared to SRAM.
Therefore, use of MCP with the memory using the memory cells of DRAM embedded in place of the conventionally embedded SRAM would increase the consumption current at stand-by, and hence is inappropriate as a memory directed to a portable information terminal operating by a battery with the strict requirement for the reduction of consumption current.
It is an object of the present invention to provide a semiconductor memory device having a small mounting area and a large memory capacity, and capable of reducing consumption current at stand-by.
According to an aspect of the present invention, a semiconductor memory device transferring storage data with an external source includes first and second volatile memory circuits, a non-volatile memory circuit, and a package.
The first volatile memory circuit is of a first type, and receives a power-supply potential from a first power-supply node. The second volatile memory circuit is of a second type different from the first type, and receives a power-supply potential from a second power-supply node. The non-volatile memory circuit receives a power-supply potential from a third power-supply node. The package encloses the first and second volatile memory circuits and the non-volatile memory circuit.
Therefore, a main advantage of the present invention is that the power-supply nodes are separately provided so that consumption current at stand-by can be reduced.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.